Turbochargers with waste gate valves have previously been described. A turbocharger serves to increase the boost pressure and thus to increase the power of the internal combustion engine. The pressure which can be generated is always a function of the exhaust gas quantity conveyed due to the turbine wheel being coupled with the compressor wheel. It is therefore necessary to reduce or control the drive power acting on the compressor under certain operating conditions.
Waste gate valves are used therefor, among others, which valves are arranged in a bypass channel via which the turbine can be bypassed so that the turbine wheel is no longer acted upon by the entire flow quantity of the exhaust gas. These waste gate valves are most often designed as flap valves operated by a pneumatic actuator which drives a linkage coupled with the flap.
Since a high thermal load exists in the region of the turbine housing due to hot exhaust gases, these pneumatic actuators have been arranged in the region of the compressor, and in particular at a distance from the turbine housing, in order to reduce thermal load.
An exact control of the exhaust gas quantity discharged via the bypass channel is, however, difficult to achieve with a pneumatic actuator. Electric motors have therefore seen widespread use as drives for waste gate valves in recent years. These were typically also arranged at a distance from the turbine housing to reduce thermal load so that linkages were still used for coupling with the flap.
Because of ever decreasing available installation space, it is desirable to arrange the actuators of the waste gate valves in the immediate proximity to the valve itself since the installation space necessary is thus reduced and a more precise control becomes possible. When linkages are used, an increased wear of the mechanical components, in particular due to increased transverse forces in the region of the flap bearings, as well as increased assembly efforts, often also occur.
WO 2012/089459 A1 therefore describes a turbocharger with a water-cooled turbine housing and an integrated electric waste gate valve. The housing in which the electric motor for driving the waste gate valve and the transmission are arranged is a part of the turbine housing in which corresponding cooling channels are formed to carry water. The electric motor and the transmission are thus mounted on the turbine housing, wherein the necessary opening in the turbine housing is closed with a cover. The bearing of the valve is also arranged in the turbine housing.
The use of the above waste gate valve arrangement still risks a thermal overload of the actuator since the cooling medium is strongly heated while flowing through the turbine housing and is therefore not immediately effective at the actuator. The actuator is also subjected to a direct thermal radiation from outside so that, under unfavorable conditions, a risk of overheating still exists.
The arrangement of the electric motor directly in the turbine housing generally leads to thermal overload. A relatively large installation space is also required in the axial direction of the output shaft despite the integration of the actuator into the turbine housing.